A Satellite is defined as: “an artificial body placed in orbit around the earth or other planet in order to collect information for communication”
There are three principle categories of satellite based on how high above the earth they are placed.
Geo-Stationary Earth orbit (GSO) – Approximately 22,200 miles above the equator. Orbits at the same speed as the earth thus maintaining the same position above the ground at all times.
GSO’s are owned and operated by the large satellite operators such as Inmarsat and Eutelsat, Government bodies and broadcasters like Sky TV.
Services available on GSO’s are typically broadband data such as Inmarsat’s BGAN service, and many other operators provide VSAT (Very Small Aperture Terminal) data services at varying data rates globally.
Medium Earth Orbit (MEO) – Approximately 12,500 miles above the surface of the earth. These satellites usually orbit faster than the rotational speed of the earth meaning they will come in and out of coverage as they rotate.
MEO’s are most often used for GPS location satellites and other communications services.
Low Earth Orbit (LEO) – Between 99 and 1,200 miles above the surface of the earth. Like MEO’s the orbital period of LEO’s is much faster often less than 2 hours.
The best known user of LEO satellite constellations is Iridium. A constellation of 50+ satellites orbiting the globe. Often a specific satellite will only be ‘in-view’ over your location for a matter of minutes. For this reason, calls are ’handed-off’ between satellites in much the same way as mobile phone calls are transferred between cell sites when you move from one to the other.